1. Field of the Invention
The present invention relates to a magnetic film used as a high density recording medium and a method of manufacturing the magnetic film.
2. Description of the Related Art
In recent years, magnetic recording media are required to provide ever increasing recording densities. As a technology for achieving a high recording density, known is a so-called vertical magnetic recording medium in which, for example, magnetic crystals are separated and the magnetic recording axis is made perpendicular to the substrate surface. In the particular magnetic recording medium, the magnetic bodies are arranged independently on the substrate and the interference of the magnetic domains is suppressed so as to maintain stable the magnetic properties of each magnetic domain. As a result, it is possible to obtain the merit that the recorded information can be retained stable over a long period of time.
A conventional magnetic film is proposed in, for example, “Watanabe et al., J. Magn. Magn. Mater., 177/181, 1231 (1998)”. Specifically, proposed is a magnetic film of the construction in which an Fe film and a Pt film are laminated, respectively, by the vapor deposition on a substrate of magnesia (MaO), followed by further forming an Fe—Pt thin film by the vapor deposition on the laminate film. The particular method makes it possible to form a magnetic recording medium exhibiting a strong coercive force required for the magnetic recording at a high density. In this magnetic recording medium, the crystal axis of the Fe—Pt is controlled to form an axis adapted for vertical magnetization.
On the other hand, JP-A 2003-289005 (KOKAI) teaches that a magnetic recording medium is manufactured by depositing Fe—Pt on an MgO substrate by a sputtering method so as to form a granular product on the substrate. The method disclosed in this prior art is advantageous in that it is possible to omit the step of forming Fe films and Pt films in multi-stages.
Also, JP-A 2004-11050 (KOKAI) discloses a magnetic film prepared by forming a granular magnetic body on a substrate. It is disclosed in this prior art that a granular structure including fine particles consisting of Fe—Pt alloy is formed on a matrix consisting of MgO. According to the method disclosed in this prior art, the granular Fe—Pt alloy particles can be made finer so as to make it possible to obtain a magnetic film capable of magnetic recording at a high density.
Further, a magnetic film obtained by arranging a magnetic body of Fe—Pt alloy on a silicon substrate or a glass substrate is proposed in, for example, “Shouheng Sun et al., SCIENCE 287, 1989-1992 (2000)”. The particular magnetic film makes it possible to lower the manufacturing cost because it is possible to use a cheap substrate for manufacturing the magnetic film.
JP-A 2001-358296 (KOKAI) discloses a method of forming separated magnetic crystals on a substrate by removing a uniform magnetic crystalline film formed on a substrate. The uniform magnetic crystalline film is removed from the substrate by means of etching that uses a mask of a prescribed shape. JP-A 2003-289005 (KOKAI) referred to previously also teaches that a granular product is formed on a substrate by a sputtering method. The latter method makes it possible to omit the step of peeling off the magnetic crystal and, thus, wastage of the magnetic material can be avoided.
Further, it is also described in the literature by Shouheng et al. referred to above that island-shaped crystalline bodies are formed on a substrate by coating the substrate with Fe—Pt particles synthesized separately in advance. In this method, it is unnecessary to use a sputtering apparatus and, thus, a magnetic film can be formed easily at a low cost.
As described above, disclosed are various magnetic films having granular FePt materials. In these magnetic films, however, MaO that is deliquescent is used as the substrate material, with the result that the substrate is deformed by water. The deformation of the substrate causes the granular crystalline formed on the substrate to be also deformed at the same time so as to make the magnetic recording unstable. As a result, it is necessary to form a protective film for preventing water from entering the magnetic film. The gap between the head for the magnetic recording in a magnetic film and the magnetic film is increased by the formation of the protective film, with the result that the magnetic information tends to be deteriorated. Also, in the manufacturing process of the magnetic film, it is necessary to employ the step for removing water in order to suppress the deformation of the surface of the substrate made of MaO. It follows that the manufacturing cost of the magnetic film is increased.
On the other hand, deformation caused by water as in the MgO substrate is not generated in the silicon substrate or the glass substrate. However, it is difficult to allow the crystal axis of the FePt alloy to be arranged in a direction adapted for the vertical recording. Such being the situation, an excessive FePt crystalline is required for ensuring a prescribed recording capacity so as to increase the manufacturing cost.
Under the circumstances, it is proposed for the magnetic body positioned on the substrate to be formed of an FePt alloy. The FePt alloy is known to exhibit a strong coercive force. However, the alloy composition of the FePt alloy exhibiting a strong coercive force is limited. To be more specific, an L10 phase is formed in the region where the Fe content is about 50 atomic % so as to exhibit the strongest coercive force, as shown in the phase diagram of the FePt alloy shown in FIG. 4. The coercive force of the alloy is rapidly lowered with deviation of the Fe content from 50 atomic %. Where the magnetic film is applied to a magnetic recording medium, it is difficult to obtain a magnetic recording medium having a desired recording density, if the island-shaped magnetic body deviates from the prescribed composition ratio in the plane of the magnetic recording medium.
In a method of depositing FePt particles on a substrate by, for example, sputtering, the island-shaped magnetic body can be formed excessively on the substrate. Therefore, it is possible to obtain a magnetic recording medium having a desired recording density, even if the island-shaped magnetic body deviates from the prescribed composition ratio. However, the FePt particles deposited by this method are rendered nonuniform in size, with the result that non-uniformity in the recording density is generated by the change in size of the particles of the magnetic body.